Up to now, lipid vesicles have been the system of choice for the development of artificial cells (Chiarabelli, C., Stano, P. & Luisi, P. L. Curr Opin Biotechnol 20, 492-497 (2009); Noireaux, V., Maeda, Y. T. & Libchaber, A. Proc Natl Acad Sci USA 108, 3473-3480 (2011); Szostak, J. W., Bartel, D. P. & Luisi, P. L. Nature 409, 387-390 (2001)). However, the small size of these compartments limits their manipulation, including the ability to measure ionic currents through the bilayer envelopes.
Systems based on droplet interface bilayers (DIB) can be more readily controlled (Holden, M. A., Needham, D. & Bayley, H. J Am Chem Soc 129, 8650-8655 (2007)). A DIB is formed when two lipid-monolayer coated droplets in an oil are brought together. Several such droplets can be assembled to form a network, and when membrane proteins are included in the DIBs, functional systems are produced (Holden, M. A., Needham, D. & Bayley, H. J Am Chem Soc 129, 8650-8655 (2007)). DIBs have been used to study the fundamental properties of membrane proteins (Leptihn, S., Thompson, J. R., Ellory, J. C., Tucker, S. J. & Wallace, M. I. J Am Chem Soc 133, 9370-9375 (2011); Harriss, L. M., Cronin, B., Thompson, J. R. & Wallace, M. I. J Am Chem Soc 133, 14507-14509 (2011); Heron, A. J., Thompson, J. R., Mason, A. E. & Wallace, M. I. J Am Chem Soc 129, 16042-16047 (2007); Bayley, H. et al. Mol BioSystems 4, 1191-1208 (2008); Syeda, R., Holden, M. A., Hwang, W. L. & Bayley, H. J Am Chem Soc 130, 15543-15548 (2008); Heron, A. J., Thompson, J. R., Cronin, B., Bayley, H. & Wallace, M. I. J Am Chem Soc 131, 1652-1653 (2009)), and DIB networks have been used to construct devices (Bayley, H. et al. Mol BioSystems 4, 1191-1208 (2008)), including a light sensor (Holden, M. A., Needham, D. & Bayley, H. J Am Chem Soc 129, 8650-8655 (2007)), a battery (Holden, M. A., Needham, D. & Bayley, H. J Am Chem Soc 129, 8650-8655 (2007)), and half- and full-wave rectifiers (Maglia, G. et al. Nat Nanotechnol 4, 437-440 (2009)). Recently, droplet networks that function in aqueous media have been devised (Villar, G., Heron, A. & Bayley, H. Nat Nanotechnol 6, 803-808 (2011)). In a synthetic biology context, these networks can be regarded as minimal tissues (prototissues) (Woolfson, D. N. & Bromley, E. H. C. The Biochemist February, 19-25 (2011)).
Networks based on aqueous droplets can be delicate, which can limit their application. There is thus an ongoing need to develop more robust networks for a wide variety of application areas, including the area of synthetic biology. For example, robust 3-dimensional systems that incorporate engineered membrane proteins for inter-compartment communication are required.